<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .content{
            position: relative;
            width: 100px;
            height: 100px;
            border: 1px solid #000000;
        }
        .box{
            position: absolute;
            left: 0;
            bottom: 0;
            width: 0;
            height: 0;
            border: 6px solid transparent;
        }
        .b1{
            border-bottom-color:#000;
        }
        .b2{
            border-bottom-color:#fff ;
        }

    </style>
</head>

<body>
    <div class="content" id="btn">
        <div class="box b1"></div>
        <div class="box b2"></div>
    </div>
    <script>
        document.getElementById('btn').onclick=function(){

            // window.sessionStorage.setItem('a','bbbb')
            window.Cookies.get('name');
        }
        window.onload = function () {
            var millisecond = new Date().getTime();
            var expiresTime = new Date(millisecond + 60 * 1000 * 15);
            
            document.Cookies.set('name', 'value', {
                expires: expiresTime,
            });
        }
    </script>
</body>
</html>